Macrocyclic ketones represented by the following formula (I) have a musk aroma and are useful as perfumes or bases for perfumes: ##STR1## wherein n is an integer of from 12 to 18.
It is known that these macrocyclic ketones can be prepared by the following reaction scheme as described in Helv. Chem. Acta., 30, 1741 (1947) and Arther C. Cope et al., Organic Synthetis, 218 (1963): ##STR2## wherein n is as defined above; and R represents an alkyl group having from 1 to 4 carbon atoms.
According to this known process, the acyloin condensation (reaction A) is carried out in a sodium-aromatic hydrocarbon solvent system. After the reaction, an alkanol is added to the reaction mixture to convert unreacted sodium to a sodium alkoxide. The mixture is then neutralized with dilute sulfuric acid, and the aqueous phase is separated. The aromatic hydrocarbon solvent solution is washed successively with a sodium carbonate aqueous solution and water, dried and distilled under reduced pressure to isolate the compound represented by the formula (II). The resulting compound (II) is then reduced (reaction B) with zinc-hydrochloric acid in a glacial acetic acid solvent to thereby obtain the compound (I).
Since the above-described known process employs different solvents between reaction A (acyloin condensation) and reaction B (reduction), the process inevitably involves the isolation of the acyloin condensation product, which makes the process complicated and reduces the production efficiency. Moreover, use of glacial acetic acid in reaction B allows for a conversion rate near 100% but also tends to cause an excessive reduction to co-produce a large amount of cycloalkanes, resulting in low selectivity to macrocyclic ketones. As a result, the resulting macrocyclic ketones have reduced purity, which will be a bar to final use as perfumes and the like. Further, in the above-described process, the isolation of the resulting macrocyclic ketones after reduction is troublesome. For example, in the above-cited process, the macrocyclic ketones should be extracted with organic solvents that are incompatible with water, e.g., diethyl ether, and after washing the extract with water to remove water-soluble inorganic materials, recovered from the extract by distillation.